Image forming system that inspects quality of an image formed on a sheet

ABSTRACT

A first surface of a first sheet has a second image formed in advance. An image forming system generates reference data based on a result of reading an image on the first surface of the first sheet on which a first image is not formed, generates first image data that represents a result of reading an image on the first surface of the first sheet having the first image formed on the first surface, and determines, based on the reference data and the first image data, a relative position between the first image and the second image on the first surface of the first sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2021-050385, filed Mar. 24, 2021, and Japanese Patent Application No.2022-021434, filed Feb. 15, 2022, which are hereby incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image forming system that inspectsthe quality of an image formed on a sheet.

Description of the Related Art

In recent years, it has become required to inspect the quality of animage formed on a sheet. Japanese Patent Laid-Open No. 2005-238817proposes printing another image on a sheet (preprinted sheet) on whichan image is printed in advance, and inspecting the print quality of theother image. According to Japanese Patent Laid-Open No. 2005-238817, thepreprinted sheet is read by an image sensor in advance to generatereference data. Subsequently, the other image is additionally formed onthe preprinted sheet and read by the image sensor, then, inspection datais generated. Finally, the print quality is determined based on thereference data and the inspection data.

Meanwhile, according to Japanese Patent Laid-Open No. 2005-238817, anarea where an image is preprinted is masked, and the print quality isdetermined for an area of the entire area of the sheet excluding themasked area. In other words, according to Japanese Patent Laid-Open No.2005-238817, relative position between the image preprinted on the sheetand the image additionally printed on the sheet is not taken intoconsideration. Thus, according to Japanese Patent Laid-Open No.2005-238817, the inspection may result in a good result even when thepositional relationship between the image preprinted on the sheet andthe image additionally printed on the sheet is inappropriate.

SUMMARY OF THE INVENTION

The present invention provides an image forming system comprising animage forming unit configured to form a first image on a first surfaceof a first sheet, the first surface of the first sheet having a secondimage formed in advance, a reading unit provided on a downstream side ofthe image forming unit in a conveyance direction in which the firstsheet is conveyed and configured to read an image on the first sheetconveyed, and at least one processor configured to generate referencedata based on a result of reading, by the reading unit, an image on thefirst surface of the first sheet on which the first image is not formed,to generate first image data that represents a result of reading, by thereading unit, an image on the first surface of the first sheet havingthe first image formed on the first surface by the image forming unitand to determine, based on the reference data and the first image data,a relative position between the first image and the second image on thefirst surface of the first sheet on which the first image is formed.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of an image inspection system;

FIG. 2 is an explanatory view of a control device;

FIG. 3 is an explanatory view of an image inspection device;

FIGS. 4A to 4C are explanatory views of edge enhancement processing;

FIGS. 5A to 5C are explanatory views of binarization processing;

FIGS. 6A to 6C are explanatory views of processing of determining acharacter area;

FIGS. 7A and 7B are explanatory views of a setting screen;

FIGS. 8A and 8B are explanatory views of image inspection;

FIG. 9 is a flowchart illustrating an image inspection method;

FIG. 10 is a flowchart illustrating an image inspection method; and

FIG. 11 is an explanatory view of an image inspection system.

DESCRIPTION OF THE EMBODIMENTS

Hereafter, embodiments will be described in detail with reference to theattached drawings. Note, the following embodiments are not intended tolimit the scope of the claimed invention. Multiple features aredescribed in the embodiments, but limitation is not made to an inventionthat requires all such features, and multiple such features may becombined as appropriate. Furthermore, in the attached drawings, the samereference numerals are given to the same or similar configurations, anda redundant description thereof is omitted.

Image Forming System

An image forming system 100 according to the present embodiment isdescribed below. As illustrated in FIG. 1 , the image inspection system(image forming system) 100 includes an operation unit (operation panel)20, an image formation device 30, a control device 40, an imageinspection device 50, a stacker device 60, and a post processing device70.

The operation unit 20 includes a display device that outputs informationto the user and an input device (touch panel sensor for example) thataccepts instructions from the user.

The image formation device 30 forms a toner image on a sheet P based ona YMCK color signal supplied from the control device 40. The charactersYMCK attached to reference numerals respectively represent yellow,magenta, cyan, and black that are toner colors. In descriptions commonto the four colors, the characters YMCK are not attached to thereference numerals.

A photosensitive member 1 is an image bearing member that bearselectrostatic latent images and toner images. A charging unit 2uniformly charges a surface of the photosensitive member 1. An exposureunit 3 irradiates a photosensitive member 1Y with a laser beamcorresponding to a color signal supplied from the control device 40 toform an electrostatic latent image on the surface of the photosensitivemember 1. A development unit 4 develops the electrostatic latent imageusing toner to form a toner image on a surface of the photosensitivemember 1. A primary transfer roller 5Y transfers the toner image, formedon the surface of the photosensitive member 1, from the photosensitivemember 1 to an intermediate transfer belt 6. Here, each of YMCK tonerimages is superimposed to form a color image. The intermediate transferbelt 6 conveys the toner images to a secondary transfer unit 7.

A sheet cassette 11 is a stocker that stores a large number of sheets P.Here, the sheets P stored in the sheet cassette 11 may each be apreprinted sheet that is a first sheet. The preprinted sheet is a sheeton which an image is formed in advance by the image formation device 30,other image formation devices, or the like. Typical examples of thepreprinted sheet include a bill, a delivery slip, and the like. In thefollowing, a case where the sheets P stored in the sheet cassette 11 arepreprinted sheets will be described.

Conveyance rollers 12 feed the sheet P stored in the sheet cassette 11,and conveys the sheet P along a conveyance path.

The secondary transfer unit 7 transfers the toner images from theintermediate transfer belt 6 to the sheet P. A fixing unit 8 appliesheat and pressure to the sheet P and the toner images, to fix the tonerimages on the sheet P. Discharge rollers 17 discharge the sheet P to theimage inspection device 50.

The image inspection device 50 is a device configured to inspect thequality of an image formed on the sheet P. An inspection controller 51reads the sheet P using an image sensor 52 a and an image sensor 52 bwhile conveying the sheet P using conveyance rollers 53. The imagesensors 52 a and 52 b each includes a light source that illuminates thesheet P and a complimentary metal-oxide-semiconductor (CMOS) sensor. Theinspection controller 51 generates image data corresponding to theresult of reading the sheet P by the image sensors 52 a and 52 b.

The stacker device 60 conveys the sheet P, discharged from the imageinspection device 50, using conveyance rollers 63. The stacker device 60includes an NG tray 62 and a large-capacity tray 61. The sheet P theimage quality of which is determined to be not good by the imageinspection device 50 is stacked on the NG tray 62, for example. Thecontrol device 40 controls the image formation device 30 to form animage, which was formed on the sheet P and determined to be not good(NG) by the image inspection device 50, on a new sheet P (reprinting).The control device 40 may display an NG (not good) determination by theimage inspection device 50 on a display device 21, to notify a user ofthe NG result.

The large-capacity tray 61 is a sheet stacking unit on which a largenumber of sheets P can be stacked. The stacker device 60 includesflappers 64 a and 64 b that switch the destination of the sheet P. Thecontrol device 40 controls the flappers 64 a and 64 b based on a printjob and the image inspection result. The control device 40 may controlthe flappers 64 a and 64 b to output the sheet P to the post processingdevice 70.

The post processing device 70 conveys the sheet P using a plurality ofconveyance rollers 73. The post processing device 70 includes an uppertray 74 a, a middle tray 74 b, and a lower tray 74 c as sheet dischargetrays. The control device 40 controls flappers 72 a and 72 b todischarge the sheet P onto any of the upper tray 74 a, the middle tray74 b, and the lower tray 74 c. The post processing device 70 may includea binding processing machine that bundles the sheets P, discharged fromthe stacker device 60, to make a sheet bundle, and staples and binds thesheet bundle. The post processing device 70 may include a bookbindingmachine that folds the sheet bundle in two. The post processing device70 may include a cutting machine that cuts the sheet bundle.

In the present embodiment, the sheets P determined to be good by theimage inspection device 50 are stacked on the large-capacity tray 61, orare processed into a sheet bundle by the post processing device 70.According to known techniques, when one sheet P in a sheet bundleincluding hundreds of sheets P is determined to be not good, the entiresheet bundle is discarded. On the other hand, with the presentembodiment, the sheet P determined to be not good is excluded from thesheet bundle, whereby the sheet bundle would not be wasted. Thus, thepresent embodiment contributes to the effective resource utilization.

Next, a control configuration in the image forming system 100 will bedescribed. FIG. 2 illustrates details of the control device 40. A CPU201 realizes a plurality of functions by executing a control program 213stored in a memory 210. The CPU 201 may include a plurality ofprocessors or CPU cores. Some or all of the plurality of functionsrealized by the CPU 201 may be realized by a hardware circuit differentfrom the CPU 201. The memory 210 is a storage device including a readonly memory (ROM), a random access memory (RAM), a solid state drive(SSD), a hard disk drive (HDD), and the like.

FIG. 3 illustrates details of the inspection controller 51. A CPU 301realizes a plurality of functions by executing a control program 313stored in a memory 310. Some or all of the plurality of functions may berealized by a hardware circuit. The memory 310 is a storage deviceincluding a ROM, a RAM, an SSD, an HDD, and the like.

A UI display unit 203 of a setting unit 202 displays a user interface(UI) required for image inspection settings, on the display device 21 ofthe operation unit 20. A reception unit 204 of the setting unit 202accepts an operation or instruction on the user interface from an inputdevice 22.

Reference Data Generation

A method of generating reference data 211 serving as a reference imagefor image inspection will be described below.

When the instruction to generate the reference data 211 is input to thecontrol device 40 via the display device 21, the control device 40controls the image formation device 30 to convey the sheet P that is apreprinted sheet stored in the sheet cassette 11. Note that when thesheet P is conveyed to generate the reference data 211, the imageformation device 30 does not form an additional image on the sheet P,the additional image is a first image to be formed by the imageformation device 30 in an inspection job described later.

When the instruction to generate the reference data 211 is input to thecontrol device 40 via the display device 21, the control device 40controls the image inspection device 50 to read the image on the sheet Pconveyed from the image formation device 30.

The inspection controller 51 generates the reference data 211 based onthe image data that is a result of the image sensors 52 a and 52 breading the sheet P conveyed thereto without having the image formedthereon by the image formation device 30, and stores the reference data211 in the memory 310. Note that the inspection controller 51 maygenerate the reference data 211 based on an average value of the imagedata (pixel values) of a plurality of sheets P read by the image sensors52 a and 52 b.

The control device 40 receives the reference data 211 from theinspection controller 51 and stores the reference data 211 in the memory210. The UI display unit 203 may display the image represented by thereference data 211 on the display device 21.

Image Inspection

Next, a method of inspecting an image based on the reference data 211will be described. Note that, in the present embodiment, after thereference data 211 is generated, the inspection job starts (that is, anadditional image is formed on the sheet P stacked on the sheet cassette11). However, this should not be construed in a limiting sense.

The control device 40 stores, in the memory 210, inspection setting data212 that is information on image inspection set by the user via thedisplay device 21. The control device 40 transfers the inspectionsetting data 212 to the image inspection device 50. The inspectionsetting data 212 will be described later.

When an instruction to start the inspection job for forming an image onthe sheet P and inspecting the image formed is input to the controldevice 40 via the display device 21, the control device 40 controlsvarious devices such as the image formation device 30, the stackerdevice 60, and the post processing device 70.

Specifically, the control device 40 controls the image formation device30 to convey the sheet P that is a preprinted sheet stored in the sheetcassette 11. Furthermore, the control device 40 controls, for example,the image formation device 30 to print an image, corresponding to imagedata input from an external device such as a PC or a tablet, on thesheet P.

A conveyance control unit 306 provided to the inspection controller 51drives a motor M2 to rotate the conveyance rollers 53. A reading controlunit 307 provided to the inspection controller 51 controls the imagesensors 52 a and 52 b to read the sheet P and to generate image data.The image sensor 52 a reads a first surface of the sheet P, and theimage sensor 52 b reads a second surface of the sheet P on the sideopposite to the first surface. Thus, with the present embodiment, theimage inspection can be executed on both surfaces of the sheet P.

The stacker device 60 drives a motor M1 in accordance with a controlinstruction from the control device 40, to rotate the conveyance rollers63. The stacker device 60 drives solenoids 65 a and 65 b in accordancewith the control instruction from the control device 40 to switch theflappers 64 a and 64 b. As a result, the sheet P is guided and conveyedto any of the NG tray 62, the large-capacity tray 61, or the postprocessing device 70. For example, when the result of the imageinspection by the image inspection device 50 is NG, the control device40 controls the stacker device 60 to discharge the sheet P, determinedto be NG, to the NG tray 62. The image formation device 30 and the postprocessing device 70 also include a solenoid that drives a flapper and amotor that drives a conveyance roller.

Position Correction Unit

A position correction unit 303 of an inspection unit 302 performsposition correction for the result of reading by the image sensors 52 aand 52 b. When the sheet P is read by the image sensors 52 a and 52 bwhile being skewed, the sheet P may be skewed in the read image. Also,the leading edge of the sheet P may be deviated from the ideal positionin the read image. Thus, the position correction unit 303 corrects theposition of the read image by rotating the read image, or shifting theposition of the read image to make the position of the leading edge ofthe sheet P in the read image match the ideal position.

Overlap Determination Unit

An overlap determination unit 304 determines, based on the referencedata 211 and inspection image data 312 that is image data after thecorrection by the position correction unit 303, whether a preprintedimage that is a second image printed on the sheet P before an image isformed on the sheet P by the image formation device 30 in the inspectionjob overlaps with the image (after here, referred to as an additionalimage) that is formed on the sheet P by the image formation device 30 inthe inspection job. For example, whether an additional image of acharacter overlaps with respect to a preprinted image of a ruled lineand a character is determined. Specifically, the overlap determinationunit 304 calculates, for example, a difference between the pixel value(luminance value) in the reference data 211 and the pixel value in theinspection image data 312, and determines whether the images overlapbased on the difference. More specifically, the overlap determinationunit 304 determines that the additional image of a character overlapswith the preprinted image of a ruled line or a character, when thedifference between the pixel values of the reference data 211 and theinspection image data 312 is equal to or greater ager than a firstpredetermined value. The overlap determination unit 304 determines thatthe additional image of a character does not overlap with the preprintedimage of a ruled line or a character, when the difference between thepixel values of the reference data 211 and the inspection image data 312is less than the first predetermined value. This is based on acharacteristic that the pixel value in a portion where the additionalimage of a character overlaps with the preprinted image of a ruled lineand a character is smaller than the pixel value in a portion where theadditional image of a character does not overlap with the preprintedimage of a ruled line and a character.

Displacement Determination Unit

When the additional image of a character does not overlap with thepreprinted image of a ruled line and a character, a displacementdetermination unit 305 determines whether the additional image of acharacter area is displaced with respect to the preprinted image of aruled line, and the like, by a predetermined amount or more.Specifically, for example, the displacement determination unit 305calculates the distance between the preprinted image of a ruled line andthe additional image of a character area, and determines that theadditional image of the character area is displaced with respect to thepreprinted image of the ruled line, and the like, when the distanceexceeds a second predetermined value. The displacement determinationunit 305 determines that the additional image of a character area is notdisplaced with respect to the preprinted image of a ruled line, and thelike, when the distance between the preprinted image of the ruled lineand the additional image of the character area does not exceed thesecond predetermined value. Note that, if the distance is within apredetermined range, the displacement may be determined to be tolerable.If the distance does not fall within the predetermined range, thedisplacement may be determined to be intolerable.

A method of detecting a character area performed by the displacementdetermination unit 305 will be described below.

The displacement determination unit 305 calculates an average luminancevalue in a predetermined area (for example, an area that is 7 pixels inan X direction and 7 pixels in a Y direction), based on luminance valuesincluded in the image data. The coordinate of a pixel of interest in amain scanning direction, which is a direction in which light-receivingelements of the image sensors 52 a and 52 b are arranged, is defined asX. The coordinate of the pixel of interest in a sub scanning directioncorresponding to the conveyance direction in which the sheet P isconveyed is defined as Y. When reference is made to three pixels eachbefore and after the pixel of interest in both the main scanningdirection and the sub scanning direction, an average luminance valueAVE2 is calculated based on the following formula.

${{AVE}{{2\lbrack X\rbrack}\lbrack Y\rbrack}} = {\frac{1}{49} \times {\overset{X + 3}{\sum\limits_{A = {X - 3}}}{\overset{Y + 3}{\sum\limits_{B = {Y - 3}}}{{{INPUT}\lbrack A\rbrack}\lbrack B\rbrack}}}}$

The displacement determination unit 305 performs edge enhancementprocessing on image data acquired, to detect a character area and adotted area in the image data. When three pixels each before and afterthe pixel of interest in both the main scanning direction and the subscanning direction are multiplied by a 7×7 filter coefficient K, aluminance value EDGE of the image data after the edge enhancement iscalculated based on the following formula.EDGE[X][Y]=Σ_(A=X−3) ^(X+2)Σ_(B=Y−3) ^(Y+3)INPUT[A][B]×K[A][B]

FIG. 4A to FIG. 4C are explanatory views of the edge enhancementprocessing. FIG. 4A illustrates an image corresponding to read data withthe background having a luminance value “200”, a diagonal line having aluminance value “150”, and an isolated point having a luminance value“190”. The size of the image is 10×10 pixels. FIG. 4B illustrates anedge enhancement filter having a size of 5×5 pixels. FIG. 4C illustratesa luminance value of image data after performing convolution calculationprocessing based on the edge enhancement filter. Values as a result ofconvolution processing that are equal to or less than zero are clippedto “0”. Values as a result of convolution processing that are equal toor greater than 255 are clipped to “255”.

The read data (FIG. 4C) after the convolutional calculation processinghas the luminance value of the diagonal line being “255” due to the edgeenhancement. The luminance value of the background is “0” due to edgeenhancement. The edge is extracted in this manner. The isolated pointwith a small difference in luminance relative to the luminance value ofthe background is not significantly enhanced after edge enhancement, andhas the luminance value “80”.

The displacement determination unit 305 compares a difference betweenthe average luminance value AVE2 and the luminance value EDGE to athreshold THedge. The displacement determination unit 305 outputsbinarized data BIN that takes a value “1” when the difference is equalto or less than the threshold THedge. The displacement determinationunit 305 outputs binarized data BIN that takes a value “0” when thedifference is greater than the threshold THedge. With such binarizationprocessing, information such as characters clearly printed on anoriginal document, or dots of dot printing is enhanced and extracted.The displacement determination unit 305 makes binarization determinationusing the following formula.if |EDGE[X][Y]−AVE 2[X][Y]|≤TH _(edge),BIN=1else |EDGE[X][Y]−AVE 2[X][Y]|>TH _(edge),BIN=0

In the example illustrated in FIG. 4C, binarization processing isexecuted resulting in the threshold THedge being “100”, a pixel with adifference that is equal to or greater than 100 being “0”, and a pixelwith a difference being equal to or less than 99 being “1”. With thisprocessing, only the pixels including the diagonal line have the valueBIN=1, so that the diagonal line can be extracted.

The displacement determination unit 305 detects a group of pixels in anisolated state without any pixel with the value BIN=1 in the periphery,such as dots formed on the sheet P. The displacement determination unit305 prepares in advance, a pattern matching image in which an image forwhen dots are read is envisioned, and detects an area in which an imagematching the pattern matching image is found, as the group of pixels inthe isolated state. The displacement determination unit 305 changes thevalues of the binarized data BIN of the group of pixels thus detectedfrom “1” to “0”. With such processing, dotted portions can be removedfrom the binarized data.

FIG. 5A is a diagram illustrating an example of the binarized data BIN.Specifically, FIG. 5A illustrates an example of the binarized data BINincluding a character “A” and a dotted area in which 2×2 dots areprinted. FIG. 5B illustrates an example of a pattern matching image fordetecting the 2×2 dots. FIG. 5C illustrates an example of binarized dataafter the dotted area has been removed.

The binarized data BIN illustrated in FIG. 5A includes two areasmatching the pattern matching image (areas surrounded by bold frames inFIG. 5A). The binarized data in FIG. 5C is obtained by changing thebinarized data BIN of these areas from “1” to “0”.

In this example, the character “A” is remaining with the 2×2 dottedareas removed, meaning that only the character area is extracted withthe dotted areas removed. The displacement determination unit 305determines that pixels set to “1” in binarized data DOT as a result ofremoving the dotted areas as illustrated in FIG. 5C, as the characterarea.

The displacement determination unit 305 performs area mapping with animage read by the image sensor sectionalized into areas of apredetermined size (such as, for example, rectangular areas having asize of 32×32 pixels), to detect the character area. FIG. 6A to FIG. 6Care diagrams illustrating processing of determining the character area.

The displacement determination unit 305 determines whether each mappedarea includes a pixel with the binarized data DOT being “1”. Thedisplacement determination unit 305 determines the area including thepixel with the binarized data DOT being “1” as an area including a“character”. In the example illustrated in FIG. 6B, the character “A” isprinted in a range of Area 11, Area 12, Area 21, and Area 22. Theseareas include the pixels with the binarized data DOT being “1”, and,thus, a character is determined to be included in an area surrounded bya bold frame.

The method of determining the character area is not limited to themethod described above. For example, a method of determining thecharacter area using a trained model that has been trained in advancemay be used.

Inspection Content Setting

FIG. 7A illustrates an example of a print setting screen 400. FIG. 7Billustrates an example of an inspection setting UI 410. The CPU 201displays the print setting screen 400 on the display device 21, inaccordance with the control program 213. The inspection content mayindicate the inspection processing (inspection job), or may indicateconditions or information for setting or defining the inspectionprocessing.

The print setting screen 400 includes a sheet selection button 401. Whenthe sheet selection button 401 is pressed, the CPU 201 (reception unit204) accepts designation of the sheet cassette from which the sheet P isfed, the size of the sheet, and the type of sheet (cardboard, plainpaper, thin paper, gloss paper).

When an inspection setting button 402 is pressed, the CPU 201 (UIdisplay unit 203) displays the inspection setting UI 410, illustrated inFIG. 7B, on the display device 21.

When a cancel button 403 is pressed, the CPU 201 (setting unit 202)discards the contents set by the user on the printing setting screen 400and returns to an initial setting screen (not illustrated).

When a print start button 404 is pressed, the CPU 201 starts printingwithout executing the image inspection.

As illustrated in FIG. 7B, the inspection setting UI 410 includes animage display area 411 and a detail setting area 412. The image displayarea 411 is an area for displaying a reference image as an imagerepresented by the reference data 211, and accepting the setting for theinspection area as an area in which the inspection is performed in thereference image.

When a check box 420 is not checked, an image to be formed on the sheetP by the image formation device 30 is displayed in the image displayarea 411. Thus, the check box 420 is a control object for designatingthe image displayed in the image display area 411 to be the referenceimage or an image to be formed on the sheet P by the image formationdevice 30.

The detail setting area 412 changes to be operable when the check box420 is checked. Specifically, a screen for setting the inspectioncontent is displayed to accept the setting for the inspection content(condition).

A setting area 413 a includes an area setting button 414 a and a contentdesignation menu 415 a. The area setting button 414 a displays the nameof an inspection area (determination area). On the left side of the areasetting button 414 a, it is indicated that a first inspection area 421 ais to be displayed with a dashed line. When the area setting button 414a is pressed, the CPU 201 (reception unit 204) accepts the designationof the first inspection area 421 a input by the user in the imagedisplay area 411. For example, the CPU 201 (reception unit 204) sets anarea of the image display area 411 touched by the user using his or herfinger or a touch pen, to be the inspection area. For example, the CPU201 (reception unit 204) sets a coordinate system with the origin at theupper left corner of the reference image, and stores the coordinates ofthe first inspection area 421 a designated by the user, in theinspection setting data 212. The CPU 201 (UI display unit 203) mayhighlight and display the inspection area set by the user. Thehighlighted display includes surrounding the inspection area with aframe, displaying the inspection area in a strip shape, and the like.The content designation menu 415 a displays candidates for theinspection content and accepts the designation of the inspection contentby the user. The CPU 201 (reception unit 204) stores the inspectioncontent selected from the content designation menu 415 a, in theinspection setting data 212. When an add button 416 a is pressed, theCPU 201 (the UI display unit 203, the reception unit 204) additionallydisplays the second content designation menu 415 a to accept anadditional inspection content.

Setting areas 413 b and 413 c also accept the inspection setting as withthe setting area 413 a. The setting area 413 b includes an area settingbutton 414 b for accepting a second inspection area 421 b, and a contentdesignation menu 415 b. In this example, an add button 416 b has alreadybeen pressed, and two inspection contents have been set. On the leftside of the area setting button 414 b, it is indicated that the secondinspection area 421 b is to be displayed with a one-dot chain line. Inthe image display area 411, the second inspection area 421 b isdisplayed with the one-dot chain line.

A setting area 413 c includes an area setting button 414 c for acceptinga third inspection area 421 c, a content designation menu 415 c, and anadd button 416 c. On the left side of the area setting button 414 c, itis indicated that the third inspection area 421 c is to be displayedwith a two-dot chain line. The third inspection area 421 c is displayedon the image display area 411 by a two-dot chain line.

An add button 417 is a button for adding a setting area 413. Forexample, in the default state, only the setting area 413 a is displayed.When the add button 417 is pressed in this state, the CPU 201 (UIdisplay unit 203) additionally displays the setting area 413 b. When theadd button 417 is further pressed in this state, the CPU 201 (UI displayunit 203) additionally displays the setting area 413 c.

When a return button 419 is pressed, the CPU 201 (UI display unit 203)returns to the print setting screen 400. When an inspection print startbutton 418 is pressed, the CPU 201 starts the inspection job for formingan image on the sheet P and inspecting the image formed on the sheet P.

Of the inspection contents, “overlap with ruled line or character” isfor inspecting the overlap between the additional image and a ruled lineand a character included in the preprinted image. Furthermore,“displacement relative to ruled line” is for inspecting displacementbetween the additional image and the ruled line included in thepreprinted image. Furthermore, “excluded from inspection” is for notperforming inspection in the corresponding inspection area.

The displayed order of the three setting areas 413 a to 413 c displayedin this example may correspond to the priority of image inspection.Specifically, the inspection content set in the setting area 413 adisplayed on the top is preferentially executed over the inspectioncontent set in the setting area 413 b, which is second from the top. Theinspection content set in the setting area 413 b, which is second fromthe top, is preferentially executed over the inspection content set inthe setting area 413 c, which is third from the top. In the example caseillustrated in FIG. 7B, in the setting area 413 c, the entire inspectiontarget image is set to be an excluded-from-inspection area. In theexcluded-from-inspection area, the inspection areas in the setting areas413 a and 413 b are set. The priorities of the setting areas 413 a and413 b are higher than that of the setting area 413 c, and, thus, theinspection contents set in the setting areas 413 a and 413 b areexecuted.

FIG. 8A illustrates an example case when “overlap with ruled line orcharacter” is detected. The preprinted image includes characters such as“billing amount” and “yen” and/or a ruled line. The additional image isa character “5000”. In FIG. 8A, in an inspection area 501, the character“5000” overlaps with a ruled line. The CPU 201 (overlap determinationunit 304) detects the overlap by calculating the difference between theadditional image and the preprinted image.

FIG. 8B illustrates an example case when “displacement relative to ruledline” is detected. The CPU 201 (displacement determination unit 305)calculates a distance h between the additional image and the preprintedimage. If the distance h exceeds the threshold, the CPU 201(displacement determination unit 305) determines that the additionalimage is displaced relative to the preprinted image.

FIG. 9 illustrates an image inspection method executed by the CPU 201 ofthe control device 40.

In S601, the CPU 201 (setting unit 202) accepts the inspection settingthrough the inspection setting UI 410.

In S602, the CPU 201 (inspection control unit 205) determines whetherthe start of the inspection job is instructed using the inspection printstart button 418 on the inspection setting UI 410. When the start of theinspection job is instructed, the CPU 201 advances the processing toS603.

In S603, the CPU 201 (setting unit 202 or inspection control unit 205)transfers the inspection setting (inspection setting data 212) to theinspection controller 51 of the image inspection device 50.

In S604, the CPU 201 (inspection control unit 205) instructs the CPU 301of the inspection controller 51 to inspect the image formed on the sheetP.

In S605, the CPU 201 (inspection control unit 205) receives theinspection result from the CPU 301 of the inspection controller 51.

In S606, the CPU 201 (job processing unit 206) sorts the sheet P inaccordance with the inspection result. When the inspection result is notgood, the CPU 201 controls the motor M1 and the solenoids 65 a and 65 bof the stacker device 60, to make the sheet P determined to be NGdischarged to the NG tray 62.

When the inspection result is not good, the control device 40 maycontrol the image formation device 30 to resolve the factor that has ledto the not good result. Specifically, when the factor that has led tothe not good result is the overlap as illustrated in FIG. 8A, thecontrol device 40 may control the image formation device 30 to shift theformed image “5000” upward, for example.

When the factor that has led to the not good result is the displacementas illustrated in FIG. 8B, the control device 40 may control the imageformation device 30 to shift the formed image “5000” downward, forexample.

When the inspection result is good, the CPU 201 controls the motor M1and the solenoids 65 a and 65 b of the stacker device 60, to make thesheet P determined to be good discharged to the large-capacity tray 61or the post processing device 70.

FIG. 10 illustrates an image inspection method executed by the CPU 301of the image inspection device 50. The CPU 301 starts the followingprocessing upon being instructed or commanded to execute an inspectionjob from the control device 40.

In S701, the CPU 301 (inspection unit 302) receives the inspectionsetting (inspection setting data 212) from the control device 40, andstores the inspection setting in the memory 310.

In S702, the CPU 301 (inspection unit 302) executes the inspection inaccordance with the inspection setting. The inspection unit 302 executesimage inspection, in accordance with the inspection content designatedby the inspection setting data 212, in the inspection area designated bythe inspection setting data 212. For example, the inspection unit 302executes the image inspection on the sheet P, by comparing the referencedata 211 acquired from the preprinted sheet not including the additionalimage with the inspection image data 312 acquired from the sheet P. Thereference data 211 may be part of the inspection setting data 212.

In S703, the CPU 301 (inspection unit 302) transmits the inspectionresult to the CPU 201. When continuously executing the printing and theimage inspection on a plurality of sheets P, the CPU 301 repeatedlyexecutes S702 and S703.

As described above, in the present embodiment, the reference data 211 isgenerated based on the first image data obtained by reading a firstsurface of the sheet P having the preprinted image, which is the secondimage, formed on the first surface but not having the additional image,which is the first image, formed on the first surface. Based on secondimage data obtained by reading the first surface of the sheet P havingthe preprinted image, which is the second image, formed on the firstsurface and having the additional image, which is the first image,formed on the first surface and based on image data corresponding to thereference data 211, the CPU 301 detects the relative position betweenthe first image and the second image on the first surface of the sheet Pon which the first image is formed. The relative position may bedetected by detecting the overlap between the first image and the secondimage and/or by detecting the displacement of the first image relativeto the second image, for example. With this configuration, the relativeposition between the image preprinted on the sheet P and the imageadditionally printed on the sheet P can be detected (inspected). Thus,it should be possible to prevent the inspection result from becominggood when the image preprinted on the sheet P and the image additionallyprinted on the sheet P are not in appropriate positional relationship.Thus, the image inspection can be more appropriately executed comparedwith the known techniques.

In addition, in the present embodiment, the image forming system 100sets part of the preprinted sheet to be the inspection area, andexecutes the image inspection on the inspection area. With thisconfiguration, the relative position between the image preprinted on thesheet P and the image additionally printed on the sheet P can bedetected (inspected). Thus, it becomes possible to prevent theinspection result from becoming good when the image preprinted on thesheet P and the image additionally printed on the sheet P are not inappropriate positional relationship. Thus, the image inspection isappropriately executed compared with the known techniques. Furthermore,with the present embodiment, no image inspection is executed outside theinspection area, whereby erroneous detection is reduced and yield of theprint product is improved.

In the present embodiment, the inspection setting and the sheet Psorting are executed by the control device 40, and an image inspectionis executed by the image inspection device 50. However, this is merelyan example. The function of the control device 40 may be incorporatedinto the controller of the image inspection device 50 or the imageformation device 30.

In the present embodiment, the reference data 211 is generated with thesheet P, stacked on the sheet cassette 11, being conveyed to the imageinspection device 50, but this is merely an example.

For example, as illustrated in FIG. 11 , the sheet P may be conveyed tothe image inspection device 50 from an inserter device 80 providedbetween the image formation device 30 and the image inspection device 50in the conveyance direction in which the sheet P is conveyed.Specifically, the sheet P stacked on an inserter tray 81 of the inserterdevice 80 may be conveyed to the image inspection device 50 byconveyance rollers 82 and discharge rollers 87. The reference data 211is generated based on the result of reading the sheet P conveyed fromthe inserter tray 81. When the additional image is formed on the sheetP, the sheet P is conveyed from the sheet cassette 11, and the imageformation device 30 forms the additional image on the sheet P. Betweenthe image formation device 30 and the image inspection device 50 in theconveyance direction, a second conveyance guide 86 that guides the sheetP conveyed from the inserter tray 81 to the image inspection device 50joins a first conveyance guide 85 that guides the sheet conveyed fromthe image formation device 30 to the image inspection device 50.

Technical Ideas Derived from Embodiments

Aspect A1

As illustrated in FIGS. 1 and 11 , the image formation device 30 and thesecondary transfer unit 7 are an example of an image forming unit thatforms the first image (for example, the additional image) on the firstsurface of the first sheet. The second image (for example, thepreprinted image) is formed on the first surface of the first sheet inadvance. The image inspection device 50 and the image sensors 52 a and52 b are an example of a reading unit that is provided on the downstreamside of the image forming unit in the conveyance direction in which thefirst sheet is conveyed and is configured to read an image on the firstsheet conveyed. The CPU 201 and the CPU 301 are an example of at leastone processor. The at least one processor may be configured to generatereference data based on the result of reading, by the reading unit, theimage on the first surface of the first sheet not having the first imageformed. The at least one processor may be configured to generate firstimage data representing the result of reading, by the reading unit, thefirst surface of the first sheet having the first image formed on thefirst surface by the image forming unit. The at least one processor maybe configured to determine, based on the reference data and the firstimage data, relative position between the first image and the secondimage on the first surface of the first sheet having the first imageformed. Determining the relative position may include determining anoverlap between the first image and the second image and/or determiningdisplacement of the first image relative to the second image, forexample. Determining the relative position may include determining therelative positional relationship between the positions of the firstimage and the second image.Aspect A2The sheet cassette 11 is an example of a stacking unit on which thefirst sheet is stacked. The conveyance rollers 12 are an example of aconveyance unit that conveys the first sheet stacked on the stackingunit to the image forming unit. A conveyor belt may be used in additionto or instead of the conveyance rollers 12.

For the at least one processor to generate the reference data, the firstsheet may be conveyed from the stacking unit to the reading unit via theimage forming unit. In this case, the image forming unit does not form,on the first surface of the first sheet, the first image for which therelative position is to be detected by the at least one processor. Forthe at least one processor to generate the first image data, the firstsheet may be conveyed from the stacking unit to the reading unit via theimage forming unit. In this case, the image forming unit forms the firstimage on the first surface of the first sheet conveyed.

Aspect A3

As illustrated in FIG. 11 , the inserter tray 81 is an example of afirst stacking unit on which the first sheet is stacked, the firststacking unit being provided between the image forming unit and thereading unit in the conveyance direction. The conveyance rollers 82 arean example of a first conveyance unit that conveys a first sheet stackedon the first stacking unit to a reading unit. The sheet cassette 11 isan example of a second stacking unit on which the first sheet isstacked. The conveyance rollers 12 are an example of a second conveyanceunit that conveys the first sheet stacked on the second stacking unit tothe image forming unit. The first conveyance guide 85 is an example of afirst conveyance guide that guides the first sheet to be conveyed fromthe image forming unit to the reading unit. The second conveyance guide86 is an example of a second conveyance guide that guides the firstsheet to be conveyed from the first stacking unit to the reading unit.As illustrated in FIG. 11 , the second conveyance guide may be providedto join the first conveyance guide at a position between the imageforming unit and the reading unit. The at least one processor controlsthe first conveyance unit to convey the first sheet from the firststacking unit to the reading unit, for generating the reference data.The at least one processor, to generate first image data, controls thefirst conveyance unit to convey the first sheet from the second stackingunit to the reading unit via the image forming unit. The image formingunit forms the first image on the first surface of the first sheet thatis conveyed from the second stacking unit.Aspect A4The sheet cassette 11 is an example of a first stacking unit on whichthe first sheet is stacked. The conveyance rollers 12 are an example ofa first conveyance unit that conveys the first sheet stacked on thefirst stacking unit to the image forming unit. The at least oneprocessor may control the first conveyance unit to convey the firstsheet stacked on the first stacking unit to the image forming unit afterthe reference data has been generated. The image forming unit forms thefirst image on the first surface of the first sheet conveyed by thefirst conveyance unit, after the reference data has been generated.Aspect A5In Aspect A4, for the at least one processor to generate the referencedata, the first sheet may be conveyed from the first stacking unit tothe reading unit via the image forming unit. In this case, the imageforming unit does not form, on the first surface of the first sheet, thefirst image for which the relative position is to be detected by the atleast one processor. For the at least one processor to generate thefirst image data, the first sheet may be conveyed from the firststacking unit to the reading unit via the image forming unit. In thiscase, the image forming unit forms the first image on the first surfaceof the first sheet conveyed.Aspect A6In Aspect A4, the inserter tray 81 is an example of a second stackingunit on which the first sheet is stacked, the second stacking unit beingprovided between the image forming unit and the reading unit in theconveyance direction. The conveyance rollers 82 are an example of asecond conveyance unit that conveys the first sheet stacked on thesecond stacking unit to the reading unit. The first conveyance guide 85is an example of the first conveyance guide that guides the first sheetto be conveyed from the image forming unit to the reading unit. Thesecond conveyance guide 86 is an example of the second conveyance guidethat guides the first sheet to be conveyed from the second stacking unitto the reading unit. The second conveyance guide is provided to join thefirst conveyance guide at a position between the image forming unit andthe reading unit. The at least one processor controls the secondconveyance unit to convey the first sheet from the second stacking unitto the reading unit, for generating the reference data. The at least oneprocessor, to generate first image data, controls the first conveyanceunit to convey the first sheet from the first stacking unit to thereading unit via the image forming unit. The at least one processormakes the image forming unit form the first image on the first surfaceof the first sheet that is conveyed from the first stacking unit.Aspect A7The at least one processor may generate the reference data based on anaverage value of image data representing a result of reading, by thereading unit, an image on the first surface of the first sheet nothaving the first image formed, and image data obtained by reading, bythe reading unit, a surface of a second sheet not having the first imageformed. The second image is formed in advance on the surface of thesecond sheet. Thus, the reference data may be generated through astatistical method using a plurality of preprinted sheets.Aspect A8The operation unit 20 is an example of an input unit including a displayunit (for example, the display device 21) that displays an imagecorresponding to the reference data. As illustrated in FIG. 7B, and thelike, the input unit may accept selection of a determination area inwhich the relative position is to be determined, in the image displayedon the display unit. The at least one processor may detect, based on thereference data and the first image data, the relative position betweenthe first image and the second image in the determination area on thefirst surface of the first sheet having the first image formed.Aspect A9 As illustrated in FIG. 7B, and the like, the display unit mayinclude a first display area that displays an image corresponding to thereference data and a second display area that displays a screen foraccepting setting of the inspection content executed on thedetermination area.Aspect A10

The second image may be a ruled line or a character.

Aspect A11

The at least one processor may determine, as the relative position,whether the first image and the second image overlap, based on thereference data and the first image data.

Aspect A12

The at least one processor may obtain a difference in pixel valuesbetween the reference data and the first image data. The at least oneprocessor may determine whether the first image and the second imageoverlap based on the difference.

Aspect A13

The at least one processor may determine that the first image and thesecond image overlap when the difference is equal to or greater than apredetermined value. The at least one processor may determine that thefirst image and the second image do not overlap when the difference isless than the predetermined value.Aspect A14The at least one processor may determine a distance between the firstimage and the second image, as the relative position in the image on thefirst surface of the first sheet, based on the reference data and thefirst image data. The at least one processor may determine whether thedistance determined is equal to or greater than a predetermineddistance.Aspect A15The NG tray 62 is an example of a first discharge stacking unit to whichthe first sheet in which the first image and the second image aredetermined to overlap is discharged, the first discharge stacking unitbeing provided on the downstream side of the reading unit in theconveyance direction. The large-capacity tray 61 is an example of asecond discharge stacking unit to which the first sheet in which thefirst image and the second image are determined not to overlap isdischarged, the second discharge stacking unit being provided on thedownstream side of the reading unit in the conveyance direction.Aspect A16The display device 21 is an example of a notification unit that providesnotification of information indicating a result of determining, as therelative position, whether the first image and the second image overlap.Aspect A17The at least one processor may determine, as the relative position, adistance between the first image and the second image, based on thereference data and the first image data. The at least one processor maydetermine whether the distance determined is equal to or greater than apredetermined distance.Aspect A18The NG tray 62 is an example of a first discharge tray on which a sheetin which the distance is determined to be equal to or greater than thepredetermined distance, is stacked, the first discharge tray beingprovided on the downstream side of the reading unit in the conveyancedirection. The large-capacity tray 61 is an example of a seconddischarge tray on which a sheet in which the distance determined isdetermined not to be equal to or greater than the predetermined distanceis stacked, the second discharge tray being provided on the downstreamside of the reading unit in the conveyance direction.Aspect A19The display device 21 is an example of a notification unit that providesnotification of information indicating a result of determining whetherthe distance determined is equal to or greater than the predetermineddistance.Aspect B1As illustrated in FIG. 1 , and the like, the image sensors 52 a and 52 bare an example of the reading unit that reads the sheet P (for example,the preprinted sheet) on which an image is formed in advance, togenerate image data to be the reference data 211. The CPU 201 and thesetting unit 202 are an example of a setting unit that sets aninspection area (for example, the first inspection area 421 a) to partof the image on the sheet P. The image formation device 30 is an exampleof an image forming unit that forms the additional image on the sheet P.The image inspection device 50 functions as an inspection unit thatexecutes image inspection, focusing on the inspection area set by thesetting unit for the inspection data (for example, the inspection imagedata 312) and the reference data 211. The inspection data is image datagenerated, by the reading unit reading the sheet P, on which theadditional image is formed. The reference data 211 is image datagenerated by reading the sheet P on which the image is formed inadvance. In this manner, with the present embodiment, the inspectionarea is set to part of the image on the sheet P. Thus, with the presentembodiment, the image inspection can be executed more appropriately thanthe known techniques with which the inspection area is always set to bethe entire image. For example, the image inspection is executed focusingon the inspection area explicitly set by the user, and thus minor defectoutside the inspection area would not be detected. Furthermore, theimage inspection is executed focusing on the inspection area being set,and thus is appropriately executed even in a case when an image with alow density is preprinted entirely over the sheet.Aspect B2The display device 21 is an example of a display unit that displays animage of the sheet P based on the reference data 211. As illustrated asan example in FIG. 7B, the CPU 201 (setting unit 202) is configured toaccept the setting of the inspection area in a state in which the imageof the sheet is displayed on the display unit. Thus, the user can setthe inspection area appropriately or easily.Aspect B3The input device 22 is an example of a touch panel sensor provided onthe upper side of the display unit. The CPU 201 (setting unit 202) mayset the inspection area in response to a touch input detected by thetouch panel sensor. This should enable the user to set the inspectionarea easily.Aspect B4The display unit (for example, the display device 21, the inspectionsetting UI 410) may include a first display area (for example, the imagedisplay area 411) displaying an image of the sheet P. The display unit(for example, the display device 21, the inspection setting UI 410) mayinclude a second display area (for example, the detail setting area 412)displaying a user interface accepting designation of the inspectioncontent executed on the inspection area.Aspects B5 to B7The user interface may include an area (for example, the area settingbutton 414 a) displaying identification information on a firstinspection area set in the image of the sheet. The user interface mayinclude an area (for example, the content designation menu 415 a)selectively displaying a first inspection content executed on the firstinspection area. The user interface may include an area (for example,the area setting button 414 b) displaying identification information ona second inspection area set in the image of the sheet. The userinterface may further include an area (for example, the contentdesignation menu 415 a) selectively displaying a second inspectioncontent executed on the second inspection area. This should enable theuser to easily set a plurality of inspection areas and an inspectioncontent. The inspection unit (for example, the inspection unit 302) mayexecute the first inspection content set to the first inspection areapreferentially over the second inspection content set to the secondinspection area. This should enable the user to execute complicatedimage inspection utilizing the priority order.Aspects B8 and B9The user interface may include an area (for example, the area settingbutton 414 c) displaying identification information on a thirdinspection area set in the image of the sheet. The user interface mayinclude an area (for example, the content designation menu 415 c)selectively displaying the third inspection content executed on thethird inspection area. The inspection unit 302 may execute the firstinspection content set to the first inspection area preferentially overthe second inspection content set to the second inspection area and athird inspection content set to the third inspection area. Theinspection unit 302 may execute the second inspection content set to thesecond inspection area preferentially over the third inspection contentset to the third inspection area.Aspect B10The area, on the user interface, in which the inspection content isdisplayed to be selectable may be a list or a menu displaying aplurality of inspection contents as selectable candidates. This shouldenable the user to determine and to select the inspection contenteasily.Aspects B11 and B12The inspection unit 302 may determine whether the additional imageoverlaps on the image formed in advance on the sheet P, by comparing thereference data 211 and the inspection data in the inspection area. Theimage formed in advance on the sheet P may be a ruled line or acharacter, for example.Aspect B13The inspection unit 302 may obtain a difference between the referencedata 211 and the inspection data in the inspection area, and determine,based on the difference, the print quality of the additional imageformed on the sheet. This difference may be used for detecting theoverlap between the two images described above.Aspects B14 and B15The inspection unit 302 may determine whether the additional image isdisplaced relative to a ruled line formed in advance on the sheet P, bycomparing the reference data 211 and the inspection data in theinspection area. The inspection unit 302 may compare the reference data211 and the inspection data in the inspection area to obtain thedistance h between the ruled line formed on the sheet P in advance andthe additional image, and determine whether the distance h exceeds athreshold.Aspect B16The large-capacity tray 61 and the trays 74 a to 74 c are an example ofa first stacking unit on which the sheet P determined to be good by theinspection unit is stacked. The NG tray 62 is an example of a secondstacking unit on which a sheet determined to be not good by theinspection unit is stacked.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or an apparatus that reads out and executescomputer executable instructions (e.g., one or more programs) recordedon a storage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., an application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., a central processingunit (CPU), or a micro processing unit (MPU)) and may include a networkof separate computers or separate processors to read out and to executethe computer executable instructions. The computer executableinstructions may be provided to the computer, for example, from anetwork or the storage medium. The storage medium may include, forexample, one or more of a hard disk, a random-access memory (RAM), aread only memory (ROM), a storage of distributed computing systems, anoptical disk (such as a compact disc (CD), a digital versatile disc(DVD), or a Blu-ray Disc (BD)™), a flash memory device, a memory card,and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. An image forming system comprising: a printerconfigured to form a first image on a first surface of a first sheet,the first surface of the first sheet having a second image formed inadvance; an image sensor provided on a downstream side of the printer ina conveyance direction in which the first sheet is conveyed, andconfigured to read an image on the first sheet conveyed; at least oneprocessor configured: to generate reference data based on a result ofreading, by the image sensor, an image on the first surface of the firstsheet on which the first image is not formed; to generate first imagedata that represents a result of reading, by the image sensor, an imageon the first surface of the first sheet having the first image formed onthe first surface by the printer; and to determine, based on thereference data and the first image data, a relative position between thefirst image and the second image on the first surface of the first sheeton which the first image is formed; and an input unit including adisplay configured to display an image that includes the second imageand does not include the first image, wherein the input unit acceptsselection of a determination area by a user in the image displayed onthe display, the determination area being an area in which the relativeposition is to be determined, and wherein the at least one processordetermines the relative position between the first image and the secondimage in the determination area on the first surface of the first sheeton which the first image is formed, based on the reference data and thefirst image data.
 2. The image forming system according to claim 1,further comprising: a stacking tray on which the first sheet is stacked;and a conveyance roller configured to convey the first sheet stacked onthe stacking tray to the printer, wherein the printer does not form thefirst image on the first surface of the first sheet, in a case when thefirst sheet is conveyed from the stacking tray to the image sensor viathe printer for the at least one processor generating the referencedata, and wherein the printer forms the first image on the first surfaceof the first sheet conveyed, in a case when the first sheet is conveyedfrom the stacking tray to the image sensor via the image forming unitfor the at least one processor to generate the first image data.
 3. Theimage forming system according to claim 1, further comprising: a firststacking tray on which the first sheet is stacked, and provided betweenthe printer and image sensor in the conveyance direction; a firstconveyance roller configured to convey the first sheet stacked on thefirst stacking unit to the reading unit; a second stacking tray on whichthe first sheet is stacked; a second conveyance roller configured toconvey the first sheet stacked on the second stacking tray to theprinter; a first conveyance guide configured to guide the first sheetconveyed from the printer to the image sensor; and a second conveyanceguide configured to guide the first sheet conveyed from the printer tothe image sensor, wherein the second conveyance guide joins the firstconveyance guide at a position between the printer and the image sensor,wherein the at least one processor, to generate the reference data,controls the second conveyance roller to convey the first sheet from thefirst stacking tray to the image sensor, and wherein the at least oneprocessor, to generate the first image data, controls the firstconveyance roller to convey the first sheet from the second stackingtray to the image sensor via the printer, and the printer forms thefirst image on the first surface of the first sheet conveyed from thesecond stacking tray.
 4. The image forming system according to claim 1,further comprising: a first stacking tray on which the first sheet isstacked; and a first conveyance roller configured to convey the firstsheet stacked on the first stacking tray to the printer, wherein the atleast one processor controls the first conveyance roller to convey thefirst sheet stacked on the first stacking tray to the printer after thereference data has been generated, and wherein the printer forms thefirst image on the first surface of the first sheet conveyed by thefirst conveyance roller after the reference data has been generated. 5.The image forming system according to claim 4, wherein the printer doesnot form the first image on the first surface of the first sheet, whenthe first sheet is conveyed from the first stacking tray to the imagesensor via the printer for the at least one processor generating thereference data, and wherein the printer forms the first image on thefirst surface of the first sheet conveyed, when the first sheet isconveyed from the first stacking tray to the image sensor via theprinter for the at least one processor generating the first image data.6. The image forming system according to claim 1, wherein the at leastone processor generates the reference data based on an average valuebetween image data representing a result of reading, by the imagesensor, an image on the first surface of the first sheet on which thefirst image is not formed, and image data representing a result ofreading by reading, by the image sensor, an image on a surface of asecond sheet on which the first image is not formed, the surface of thesecond sheet having the second image formed in advance.
 7. The imageforming system according to claim 1, wherein the display includes afirst display area in which an image that includes the second image anddoes not include the first image is displayed, and a second display areain which a screen accepting setting by the user for content of aninspection to be executed on the determination area is displayed.
 8. Theimage forming system according to claim 1, wherein the second image is aruled line or a character.
 9. The image forming system according toclaim 1, wherein the at least one processor determines, as the relativeposition, whether the first image and the second image overlap, based onthe reference data and the first image data.
 10. The image formingsystem according to claim 9, wherein the at least one processor obtainsa difference in pixel values between the reference data and the firstimage data, and determines whether the first image and the second imageoverlap based on the difference.
 11. The image forming system accordingto claim 10, wherein the at least one processor determines that thefirst image and the second image overlap when the difference is equal toor greater than a predetermined value, and determines that the firstimage and the second image do not overlap when the difference is lessthan the predetermined value.
 12. The image forming system according toclaim 9, further comprising: a first discharge stacking tray provided onthe downstream side of image sensor in the conveyance direction, andconfigured such that the first sheet in which the first image and thesecond image are determined to overlap is discharged to the firstdischarge stacking tray; and a second discharge stacking tray providedon the downstream side of image sensor in the conveyance direction, andconfigured such that the first sheet in which the first image and thesecond image are determined not to overlap is discharged to the seconddischarge stacking tray.
 13. The image forming system according to claim9, further comprising a notification display configured to displaynotification of information indicating a result of determining, as therelative position, whether the first image and the second image overlap.14. The image forming system according to claim 9, wherein the at leastone processor determines, as the relative position, a distance betweenthe first image and the second image, based on the reference data andthe first image data, and wherein the at least one processor determineswhether the distance determined is equal to or longer than apredetermined distance.
 15. The image forming system according to claim14, further comprising: a first discharge tray provided on thedownstream side of the image sensor in the conveyance direction, andconfigured such that a sheet in which the distance determined isdetermined to be equal to or longer than the predetermined distance isstacked on the first discharge tray, and a second discharge trayprovided on the downstream side of the image sensor in the conveyancedirection, and configured such that a sheet in which the distancedetermined is determined not to be equal to or longer than thepredetermined distance is stacked on the second discharge tray.
 16. Theimage forming system according to claim 14, further comprising anotification unit configured to provide notification of informationindicating a result of determining whether the distance determined isequal to or longer than the predetermined distance.